U.S. patent number 4,953,028 [Application Number 07/465,653] was granted by the patent office on 1990-08-28 for image sensor with capacitance addition means.
This patent grant is currently assigned to Fuji Photo Film Co., Ltd.. Invention is credited to Yoshimitsu Kudoh, Jin Murayama.
United States Patent |
4,953,028 |
Murayama , et al. |
August 28, 1990 |
Image sensor with capacitance addition means
Abstract
An image sensor comprising MOS-type solid-state image pickup
elements for transferring signals produced in photosensing elements
to signal read-out lines through MOS-type switches. The image
sensor is equipped with capacitance addition means comprising
MOS-type switches and capacitance elements, whereby an additive
capacitance is selectively connected to each signal read-out
line.
Inventors: |
Murayama; Jin (Kanagawa,
JP), Kudoh; Yoshimitsu (Kanagawa, JP) |
Assignee: |
Fuji Photo Film Co., Ltd.
(Kanagawa, JP)
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Family
ID: |
12507460 |
Appl.
No.: |
07/465,653 |
Filed: |
January 19, 1990 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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159087 |
Feb 23, 1988 |
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Foreign Application Priority Data
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Feb 23, 1987 [JP] |
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62-37796 |
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Current U.S.
Class: |
348/308;
250/578.1; 348/241; 348/310; 348/E3.021; 348/E3.029 |
Current CPC
Class: |
H04N
5/355 (20130101); H04N 5/374 (20130101) |
Current International
Class: |
H04N
3/15 (20060101); H04N 005/335 () |
Field of
Search: |
;358/213.31,213.11,213.15,213.18,213.27,212 ;250/578 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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70872 |
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Apr 1986 |
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JP |
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164382 |
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Jul 1986 |
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JP |
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Primary Examiner: Groody; James J.
Assistant Examiner: Bauer; Robert M.
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak &
Seas
Parent Case Text
This is a continuation of application Ser. No. 07/159,087, filed
2/23/88, now abandoned.
Claims
What is claimed is:
1. An image sensor comprising MOS-type solid-state image pickup
elements for transferring signals produced in photosensing elements
to signal read-out lines through MOS-type switches, said image
sensor further comprising reset capacitance addition means for
selectively adding a capacitance to each of said signal read-out
lines, for supplying sufficient charges required for resetting said
photosensing elements during a reset operation.
2. An image sensor as claimed in claim 1, wherein said reset
capacitance addition means comprises switching element means and a
capacitance element.
3. An image sensor as claimed in claim 2, wherein said capacitance
element comprises a condenser.
4. An image sensor as claimed in claim 2, wherein said switching
element means comprises a MOS-type switch.
5. An image sensor as claimed in claim 3, wherein said switching
element means comprises a MOS-type switch.
6. An image sensor as claimed in claim 5, wherein said image sensor
additionally comprises addition control line means for use in
selectively controlling a reset capacitive addition operation using
said reset capacitance addition means, wherein each said MOS-type
switch comprising said switching element means has a gate terminal
controlled by a voltage applied to said addition control line
means.
7. An image sensor as claimed in claim 6, wherein said reset
capacitive addition means are provided as discrete devices which
are subsequently interconnected to said signal read-out lines.
8. An image sensor comprising:
a plurality of MOS-type solid-state image pick-up elements, each
pick-up element having a photosensing element, arranged in matrix
form at the intersection of a respective one of a plurality of
first scan lines and a respective one of a plurality of second scan
lines orthogonally disposed with respect to said first scan lines,
said second scan lines being connected to a common read-out line
for transferring signals produced in said pick-up elements in
response to switching signals appearing on said first scan lines,
wherein the improvement comprises:
reset capacitance addition means, connected to said second scan
lines, for selectively adding capacitance to each of said second
scan lines, for supplying sufficient charges required for resetting
said pick-up elements during a reset operation.
9. An image sensor as claimed in claim 8 further including a
control line means and, wherein said capacitance addition means
comprises a switching element means and a capacitive element
associated with each of said second scan lines, all of said
switching element means being connected in common to said control
line means.
10. An image sensor as claimed in claim 9, wherein said control
line means is selectively activated to operate said switching
element means and to connect said capacitive elements to their
respective second scan lines.
Description
1. Field of the Invention
This invention relates to an image sensor comprising MOS-type
solid-state image pickup elements, and more particularly relates to
an image sensor equipped with charging means for supplying charges
required for resetting photosensing elements.
2. Background of the Invention
FIG. 1 shows one approach of an image sensor including a group of
photosensing elements comprising plural photodiodes arranged in a
matrix form, i.e., more particularly, there are shown vertical scan
lines V.sub.1, V.sub.2, and V.sub.3, and signal read-out lines
l.sub.1, l.sub.2, and l.sub.3, which are respectively arranged
vertically and horizontally. While only a 3.times.3 matrix is
shown, the structure may be expanded to an N.times.M configuration
as known in the art. There is also shown a plurality of respective
MOS-type switches, each of which is electrically connected to a
photosensing element, a vertical scanning line and a signal
read-out line. A switching (i.e., ON and OFF) operation of a
MOS-type switch is carried out by applying a vertical scan signal
through an appropriate vertical scan line V.sub.1, V.sub.2, and
V.sub.3, to the MOS-type switch, thereby to transfer a signal
charge produced in a photosensing element of a signal read-out line
l.sub.1, l.sub.2, and l.sub.3. Terminals of the signal read-out
lines l.sub.1, l.sub.2, and l.sub.3, are electrically connected
through MOS-type switching T.sub.H1, T.sub.H2, and T.sub.H3, to a
common signal read-out line Lc. One of the MOS-type switches
T.sub.H1, T.sub.H2, and T.sub.H3 is provided with a horizontal scan
signal and is then switched to a conductive (ON) state, so that
particular signals are read-out in a time series (S.sub.o) from the
signal read-out lines l.sub.1, l.sub.2, and l.sub.3. Before a
transfer operation, the common signal read-out line Lc is
precharged to a predetermined voltage using a power source E, so
that the signals (S.sub.o) are outputted as negative signals with
reference to the voltage E. In order to effectively utilize light
incident on the photosensing element in the image sensor, a
photoelectric conversion operation is carried out using
photo-induced charges in conjunction with a storage operation.
The photoelectric conversion operation will be described
hereinunder representatively using an exemplary picture element A,
which has been illustrated in FIG. 1 as containing a photodiode PD
and a MOS-type switch T.sub.v.
A pn junction of the photodiode PD is reversely biased and is
constructed such that incident light to the pn junction causes
charges stored in a capacitance of the junction to be discharged.
As a result, the amount of the charges in the junction is decreased
with time after the MOS-type switch T.sub.v is switched to an OFF
or equilibrium state (i.e., a state in which the capacitive
junction has been precharged to voltage E). In using this approach,
the amount of charges which are discharged within a predetermined
period is proportional to a time-integral value of incident light
within the period. As a result, a signal S.sub.o corresponding to
the amount of charges required for charging the junction up to an
initial voltage E, is outputting and then detected as a signal
proportional to the amount of the incident light.
The above approach suffers a constraint on design limitations in
that, in order to stably perform the photoelectric conversion
operation by means of the storage action of the photo-induced
charges and detect outputted signals with a high degree of
accuracy, each of the signal read-out lines l.sub.1, l.sub.2, and
l.sub.3, which feed into common output line Lc must have a large
capacitance than the junction capacitance of each photodiode.
Stated differently, in order to insure that the voltage of the
junction capacitance is precharged to thereby perform the storage
action of the photo-induced charges on the basis of the initial
voltage E, it is required that each photodiode and read-out lines
l.sub.1, l.sub.2, and l.sub.3, be so designed that the junction
capacitance of a photodiode is able to be precharged rapidly during
the periodic switching (i.e., ON and OFF) precharge operation of
the MOS switch.
For satisfying such a requirement, the signal read-out lines
l.sub.1, l.sub.2, and l.sub.3, in one approach, have been design so
as to be enlarged in width.
The above approach has been found to be unsatisfactory in several
application situations, i.e., a stable operation thereof cannot be
preformed in a case where a number of picture elements is very
small and therefore the number of photodiodes to be connected to
each signal read-out line is very small, or in a case where each
photodiode is large in size, that is, in a case where a capacitance
of each signal read-out line is not sufficiently large in
comparison with the junction capacitance of each photodiode.
Further, in a case where a number of picture elements is small,
vertical portions of the signal read-out lines (i.e., l.sub.1,
l.sub.2, and l.sub.3) must be designed so as to be short in length;
in such a situation it becomes increasingly difficult to provide
sufficient capacitance in comparison to the junction capacitance,
as the decrease in read-out line length (and therefore capacitor
plate area) results in a proportional decrease in read-out line
capacitance. The problem as described above also occurs in a case
where the shape of a photodiode is designed to be enlarged for the
improvement of a dynamic range.
As a result of the foregoing, there exists a need for an improved
image sensor approach exhibiting an improvement in dynamic range to
sufficiently ensure that the junction capacitance in a photodiode
is able to be precharged to voltage level E within the period of a
precharge operation.
SUMMARY OF THE INVENTION
In order to solve the above problem, an object according to this
invention is to provide an image sensor comprising MOS-type
solid-state images pickup elements, for transferring signals
produced in photosensing elements by a photoelectric conversion
operation thereof to signal read-out lines through MOS-type
switches, characterized by being provided with capacitance addition
means for selectively connecting capacitance elements to the signal
read-out lines.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a circuit diagram of a first approach for an image
sensor; and FIG. 2 is a circuit diagram of an image sensor
according to this invention .
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred embodiment of this invention will be described herein
with reference to the accompanying drawing.
FIG. 2 is a circuit diagram of an image sensor provided with
capacitance addition means. Components having the same operational
functions as those shown in FIG. 1 are represented by the same
reference numerals and characters.
The image sensor according to this invention has the same circuit
structure as the previously-described image sensor; however, there
is additionally provided capacitance addition means comprising, for
example, capacitance elements (condensers) C.sub.1, C.sub.2, and
C.sub.3, each of which is connected through MOS-type switches
T.sub.C1, T.sub.C2, and T.sub.C3, to one end of each of signal
read-out lines l.sub.1, l.sub.2, and l.sub.3, respectively. The
ON-OFF switching operation of each of the MOS-type switches
T.sub.C1, T.sub.C2, and T.sub.C3, is controlled by a reset signal
supplied from a reset terminal RS through a reset control signal
line L.sub.RS. As one suitable construction for the capacitance
elements C.sub.1, C.sub.2, and C.sub.3, for example, MOS-type
capacitors or the like may be used.
The operation of the image sensor according to this invention will
be described as follows.
In a case where a large capacitance is required for each signal
read-out line l.sub.1, l.sub.2, and l.sub.3, a high-level signal is
applied to the reset terminal RS to cause MOS switches T.sub.C1,
T.sub.C2, and T.sub.C3, to be at an ON or conducting state, such
that the capacitance elements C.sub.1, C.sub.2, and C.sub.3, are
connected to the signal read-out lines l.sub.1, l.sub.2, and
l.sub.3, respectively. Due to an additive effect, the capacitance
of each signal read-out line l.sub.1, l.sub.2, and l.sub.3, is
substantially increased and a junction capacitance of each
photodiode can be sufficiently charged.
In a case where the capacitance of each signal read-out line
l.sub.1, l.sub.2, and l.sub.3, is sufficiently large in comparison
with the junction capacitance of each photodiode, a low level
signal is applied to the reset terminal RS to cause the MOS
switches T.sub.C1, T.sub.C2, and T.sub.C3, to be at an OFF or
nonconducting state, whereby the signal read-out lines l.sub.1,
l.sub.2, and l.sub.3, are electrically separated from the
capacitance elements C.sub.1, C.sub.2, and C.sub.3,
respectively.
In an effort to increase an understanding of the present invention,
the followings are examples of the application of the capacitance
addition means in which the capacitance elements C.sub.1, C.sub.2,
and C.sub.3, are selectively connected to and separated from the
signal read-out lines l.sub.1, l.sub.2, and l.sub.3, as described
above.
In a first situation, where the capacitance of the signal read-out
lines l.sub.1, l.sub.2, and l.sub.3, is sufficient in comparison to
the junction capacitance of a portion of the group of photodiodes,
an image pickup operation is performed with the capacitance
elements C.sub.1, C.sub.2, and C.sub.3, being electrically
separated from the signal read-out lines.
In a second situation, where plural vertical scan lines are
simultaneously scanned (although in general a signal from the
vertical scan register scans only one scan line), the junction
capacitance is rapidly charged by connecting the capacitance
elements C.sub.1, C.sub.2, and C.sub.3, to the signal read-out
lines. The following discussion is exemplary of such a
situation.
When the signal read-out lines l.sub.1, l.sub.2, and l.sub.3, are
scanned one by one at a predetermined constant period (timing) to
perform an ordinary read-out operation, with all the vertical scan
lines scanned simultaneously, there occurs a case where presently
read-out signals are removed and then it is desired to conduct the
next image pickup operation as soon as possible. In such a case, an
interrupt operation is required which causes the vertical scan
register 1 to supply another scan signal different from the normal
scan signal to vertically scan lines V.sub.1 . . . V.sub.m, thereby
to promptly eliminate unused signals. In order to perform the
interrupt operation and the next image pickup operation, a
capacitance sufficient for charging the junction capacitances of
plural photodiodes is required for each signal read-out lines.
Accordingly, the capacitance elements C.sub.1, C.sub.2, and
C.sub.3, are electrically connected to the signal read-out lines in
synchronization with the interrupt operation, so that the junction
capacitances can be rapidly charged and the next image pickup
operation can be performed without delay.
If capacitance elements C.sub.1, C.sub.2, and C.sub.3, are not
connected to the signal read-out lines in the interrupt operation,
there exists a possibility of erroneous operation. First, it takes
a long time to charge the junction capacitances. Second, a signal
level produced in the next image pickup operation is unreliable
because the voltage of a junction capacitance of each photodiode
may not reach the initial voltage E due to insufficient
charging.
The image sensor with the capacitance addition means according to
this invention can prevent the problems as described above.
In one embodiment, the capacitance elements may be designed at the
outside of the photosensing portion, including the photosensing
elements, so that picture elements can be designed with high
density and high integration, and a degree of freedom for layout of
the device or the like on the basis of a semiconductor integration
circuit technique can be improved.
A capacitance of each capacitance element C.sub.1, C.sub.2, and
C.sub.3, is properly determined in accordance with a design
choice.
As described above, an image sensor according to this invention,
which is provided with capacitance addition means for selectively
connecting capacitance elements to signal read-out lines, can
rapidly reset the junction capacitances of photosensing elements
and thereby can be actuated or operated at a high speed.
Further, the capacitance addition means may be designed or
implemented with a simple structure at the outside of a
photosensing portion, comprising photosensing elements, and
therefore does not prevent a high density layout of photosensing
elements.
Still further, the capacitance addition means can also be used to
compensate for a lack of signal read-out line capacitance due to
the design of the high density of photosensing elements, to improve
the dynamic range of an image sensor.
* * * * *